<article id="wikiArticle">
<div></div>
<p><code><strong>lastIndexOf()</strong></code> 方法返回指定值在调用该方法的字符串中最后出现的位置，如果没找到则返回 -1。从该字符串的后面向前查找，从 <code>fromIndex</code> 处开始。</p>
<h2 id="Syntax" name="Syntax">语法</h2>
<pre><code class="language-javascript"><code><em>str</em>.lastIndexOf(<em>searchValue</em>[, <em>fromIndex</em>])</code></code></pre>
<h3 id="Parameters" name="Parameters">参数</h3>
<dl>
<dt><code>searchValue</code></dt>
<dd>一个字符串，表示被查找的值。</dd>
<dt><code>fromIndex</code></dt>
<dd>从调用该方法字符串的此位置处开始查找。可以是任意整数。默认值为 <code>str.length</code>。如果为负值，则被看作 0。如果 <code>fromIndex &gt; str.length</code>，则 <code>fromIndex</code> 被看作 <code>str.length</code>。</dd>
</dl>
<h2 id="Description" name="Description">描述</h2>
<p>字符串中的字符被从左向右索引。首字符的索引（index）是 0，最后一个字符的索引是 <code>stringName.length - 1</code>。</p>
<pre><code  class="language-javascript">"canal".lastIndexOf("a")   // returns 3
"canal".lastIndexOf("a",2) // returns 1
"canal".lastIndexOf("a",0) // returns -1
"canal".lastIndexOf("x")   // returns -1
</code></pre>
<h3 id="Example:_indexOf_and_case-sensitivity" name="Example:_indexOf_and_case-sensitivity">区分大小写</h3>
<p><code>lastIndexOf</code> 方法区分大小写。例如，下面的表达式返回 -1：</p>
<pre><code class="language-js">"Blue Whale, Killer Whale".lastIndexOf("blue"); // returns -1</code></pre>
<h2 id="Examples" name="Examples">示例</h2>
<h3 id="Example:_Using_indexOf_and_lastIndexOf" name="Example:_Using_indexOf_and_lastIndexOf">例子：使用 <code>indexOf</code> 和 <code>lastIndexOf</code></h3>
<p>下例使用 <code>indexOf</code> 和 <code>lastIndexOf</code> 方法来定位字符串 "<code>Brave new world</code>" 中的值。</p>
<pre><code class="language-js">var anyString = "Brave new world";

console.log("The index of the first w from the beginning is " + anyString.indexOf("w"));
// Displays 8
console.log("The index of the first w from the end is " + anyString.lastIndexOf("w")); 
// Displays 10

console.log("The index of 'new' from the beginning is " + anyString.indexOf("new"));   
// Displays 6
console.log("The index of 'new' from the end is " + anyString.lastIndexOf("new"));
// Displays 6
</code></pre>
<h2 id="规范">规范</h2>
<table class="standard-table">
<tbody>
<tr>
<th scope="col">Specification</th>
<th scope="col">Status</th>
<th scope="col">Comment</th>
</tr>
<tr>
<td><a class="external" href="https://www.ecma-international.org/publications/files/ECMA-ST-ARCH/ECMA-262,%201st%20edition,%20June%201997.pdf" hreflang="en" lang="en" rel="noopener" title="ECMAScript 1st Edition (ECMA-262)">ECMAScript 1st Edition (ECMA-262)</a></td>
<td><span class="spec-Standard">Standard</span></td>
<td>Initial definition.</td>
</tr>
<tr>
<td><a class="external" href="https://www.ecma-international.org/ecma-262/5.1/#sec-15.5.4.8" hreflang="en" lang="en" rel="noopener">ECMAScript 5.1 (ECMA-262)<br/><small lang="zh-CN">String.prototype.lastIndexOf</small></a></td>
<td><span class="spec-Standard">Standard</span></td>
<td> </td>
</tr>
<tr>
<td><a class="external" href="https://www.ecma-international.org/ecma-262/6.0/#sec-string.prototype.lastindexof" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">String.prototype.lastIndexOf</small></a></td>
<td><span class="spec-Standard">Standard</span></td>
<td> </td>
</tr>
</tbody>
</table>
<h2 id="浏览器兼容性">浏览器兼容性</h2>
<div><div class="blockIndicator warning"><strong><a class="external" href="https://github.com/mdn/browser-compat-data" rel="noopener">We're converting our compatibility data into a machine-readable JSON format</a></strong>.
            This compatibility table still uses the old format,
            because we haven't yet converted the data it contains.
            <strong><a class="new" href="/zh-CN/docs/MDN/Contribute/Structures/Compatibility_tables" rel="nofollow">Find out how you can help!</a></strong></div>
<div class="htab">
<a id="AutoCompatibilityTable" name="AutoCompatibilityTable"></a>
<ul>
<li class="selected"><a>Desktop</a></li>
<li><a>Mobile</a></li>
</ul>
</div></div>
<div id="compat-desktop">
<table class="compat-table">
<tbody>
<tr>
<th>Feature</th>
<th>Chrome</th>
<th>Firefox (Gecko)</th>
<th>Internet Explorer</th>
<th>Opera</th>
<th>Safari</th>
</tr>
<tr>
<td>Basic support</td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
</tr>
</tbody>
</table>
</div>
<div id="compat-mobile">
<table class="compat-table">
<tbody>
<tr>
<th>Feature</th>
<th>Android</th>
<th>Chrome for Android</th>
<th>Firefox Mobile (Gecko)</th>
<th>IE Mobile</th>
<th>Opera Mobile</th>
<th>Safari Mobile</th>
</tr>
<tr>
<td>Basic support</td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
</tr>
</tbody>
</table>
</div>
<h2 id="相关链接">相关链接</h2>
<ul>
<li><a href="Reference/Global_Objects/String/charAt" title="charAt() 方法从一个字符串中返回指定的字符。"><code>String.prototype.charAt()</code></a></li>
<li><a href="Reference/Global_Objects/String/indexOf" title="indexOf() 方法返回调用  String 对象中第一次出现的指定值的索引，开始在 fromIndex进行搜索。"><code>String.prototype.indexOf()</code></a></li>
<li><a href="Reference/Global_Objects/String/split" title="split() 方法使用指定的分隔符字符串将一个String对象分割成字符串数组，以将字符串分隔为子字符串，以确定每个拆分的位置。"><code>String.prototype.split()</code></a></li>
<li><a href="Reference/Global_Objects/Array/indexOf" title="indexOf()方法返回在数组中可以找到一个给定元素的第一个索引，如果不存在，则返回-1。"><code>Array.prototype.indexOf()</code></a></li>
<li><a href="Reference/Global_Objects/Array/lastIndexOf" title="lastIndexOf() 方法返回指定元素（也即有效的 JavaScript 值或变量）在数组中的最后一个的索引，如果不存在则返回 -1。从数组的后面向前查找，从 fromIndex 处开始。"><code>Array.prototype.lastIndexOf()</code></a></li>
</ul>
</article>